Info: 2000 Trans-Am with 59,000 miles. Oil changed regularly, rarely driven hard

Out of the blue, my car started to shutter real bad when more than probably 5% throttle was used. The car seems to idle fine at both stops and maintaining speed. I saw my gas light had come on and thought maybe the gas gauge was wrong and I was actually empty so I pulled into the closest station just to get a gallon. Problem remained and now the service engine soon light was on.

I went home and when I left to take it to the shop the gas light was on again, so this time I put about 3 gallons in it and the problem went away. I still decided to take it to the shop and they ran an engine diag on it. They said it is misfiring and the code is jumping around to each cylinder. They said that this is most likely a ECU failing, or possibly a problem with the harness. I'm gonna go pick it up for now and just pay for the diag, but what do you guys think?

 

Ive seen a couple times now at the dealership that the harness rubs on somehing, or the wires get pulled inside the harnes at the back of the inake/behind pass. head. with the eng. running, give the harness a couple light tugs, and see if it makes it misfire.
but the thing I was thinking is either you have/had bad gas or water in the tank, or, your sending unit is goin out, and giving you a false level reading, and really your running out of gas.

 

It sounds like a Ecm problem, did the shop give you the codes??? i had a similar problem when the grounds on the back of the Drivers head was loose...

 

I had a similar problem a few years ago after a header install.
Turns out water was getting into the weather pac connector for the O2 sensor and causing a bad misfire.

 

Sounds like it could be anything! Thanks for all your responses

The car seems to be running fine to me now, so we'll see what happens. They did not give me the codes, but they said that if they mis-diagnosed the problem and the ECU replacement does not fix it, then it becomes their problem to fix. So, if and when it happens again I will prob just go that route. He said that it is misfiring across ALL cylinders, like jumping around, which he said rules out the harness. So, we'll see but I guess for right now I am fine.

 

since you know it mis. on all cyl.s ,you gotta look at what they all have in common. fuel is the #1 thing I think still. or a vacuum leak will do the same thing. I just fixed a camaro this week that had the pcv tube melted and it was mis. on all cyl.s. its on the pass. side of the intake next to the throttle body. its a rubber elbow. if its melted, just replace it with a short piece of 3/8" fuel line.

 

sometimes the simpliest things are the problem check the fuel filter.

 

If the problem went away when adding 3 gallons of fuel, then it could be a fuel pump issue.

 

If it does happen again take it to auto zone or advance and they can read the code for you. I used to go there all the time to get codes read before I got my own code reader.

 

Took it to a LS1 specialty shop, they plugged their computer in and said the knock sensor was going off, and may have been causing the misfires. They had also said it could be the wiring harness or something in the computer. I left it with them and today he spent some time troubleshooting. Apparently a LOT of parts under my hood are rusted (coil packs, headlight mounts, knock sensors) and the MAF was garbage. They said the inside of the MAF was pitted like it almost had salt water in it.

I ran a carfax report and nothing showed up, so either it was flood damaged or lived the first 1/2 of it's life on the beach. It was owned by a company as a fleet car (I want to work for this company haha)...which means the dealership that I bought it from lied to me, cuz they got it from an auction. Anyways, they are replacing the knock sensors ($100 for the two) and selling me a used MAF for $120 that they just pulled off a customer car that is in perfect condition and charging me 2 hours of labor. They said that they troubleshooted the problem for a few hours, but wouldn't charge me for it. They can't guarantee this will fix the issue, but feel they are STRONG contributors to the problem.

 

I finally got this fixed a few months ago, 2nd times a charm at the dealership lol....so guess what it was
















a wire from the wiring harness was shorting out on a firewall screw. LOL.

 

was it a wire for the inj.s? Ive seen that. curious though what wire was shorted? did they tell you? it should be written on your receipt exactly what ckt/wire it was, and where on the firewall? just curious. glad someone finally got it though.